Process for forming plastic solutions and incorporating solid filling material therein



' July 18, 1944.

' CJE. BOU TWELL PROCESS FOR FORMING PLASTIC SOLUTIONS AND INCORPORATINGSOLID FILLING MATERIAL THEREIN.

Filed Sept. 2, 1941 SOLVENT .STORAGE 65 A A PUMP /0 MIX/N6 IEJJELCONDENSER "7 /4 33 M J /e /JB' 26 Z3 Z8 2/ ame/var:

ll fi 24 /7 61 ARE/veg E. Bou TWEL L1 Patented July 18, 1944 PROCESS FORFORMING PLASTIC SOLU- TIONS AND INCORPORATING SOLID FILL- ING MATERIALTHEREIN Clarence E. Boutwell, Birmingham, Ala.

Application September 2, 1941, Serial No. 409,218

' Claims. (Cl. 106-493) This invention relates to a process for therapidand thorough dispersion of plasticizers and cellulose into asolution, and for incorporating filling material into plastic solutionsand the like, such as finely divided solid material incellulosic'plastics, phenolic-aldehyde resins, while in solution, andthe like, and has for an object the provision of a process of thecharacter desi nated which shall be effective to bring about a uniformdispersion of such material, in a minimum of time, in a liquid solutionpreparatory to forming a plastic into a solid, which dispersion shall befree of lumps or masses of unwetted solid material.

In my prior Patent No. 2,219,587, issued September'28, 1940, there isdisclosed and claimed a printing plate composition comprising acellulosic plastic material and a mineral filler up to approximately 30%by volume. By using ordinary mixing methods heretoforeknown to me, ithas required from 24 to 48 hours to efiect a thorough dispersion of thefilling material in the plastic while in solution. By the process hereindisclosed I have been enabled to reduce the time required'for thoroughmixing to from 3 to 4 hours, and have obtained a better,-more completedispersion. I

In the carrying out of my invention I contemplate employing an excess ofa volatile solvent such as acetone, alcohol, or a mixture of ether andalcohol, to aid in producing the dispersion, and removing and recoveringthe ex cess solvent as mixing proceeds to completion. I furthercontemplate introducing air into the mixture along with the solidmaterial, to aid in the dispersion and to act as a vehicle in removingthe volatile solvent from the mixture.

My invention further contemplates, in its preferred embodiment, agrinding action on the materials while they are being incorporated intothe plastic solution whereby to provide a quicker, more thoroughincorporation thereof into the liquid plastic solution and to insureagainst lumps, or masses of agglomerated material passing into thesolution.

The single figure of the accompanying drawing, forming a part of thisapplication, illustrates conduit l2 controls the flow of'solvent. to thevessel. A pipe |l is'connected tothe bottom of the vessel I0 and has acontrol valve l6 therein. At I1 is a T connectionto which abranchconduit l8 for the admission of solids into the nular gear 23 andan'inside spur gear-24 with a crescent shaped projection 26extendingfrom diagrammatically, by way of example, apparatus adapted tocarry out my invention.

Referring to the drawing, I show a closed vessel l0, preferably having ahopper bottom as shown, for the mixture of solvent, plasticizers,plastic and filler. At II is shown a storage vessel for the solvent. Aconduit |2 leads from the vessel II to the vessel It, and a valve l3 inthe the casing and dividing: the space between the two gears, as shown.The solution enters the casing of the pump 22 through the conduit H at21, and is discharged at 28 into, aconduit 29 which dischargesit-backinto thevessel Ill. As will be seen in the further description ofmy inventidn, a gear pump is preferably employed, due to its grindingaction on the solid material passing therethrough. A gear pump of a formdifierentirom that herein shown may, of course,-.be employed,v so.longas it produces a circulation of the materials being mixed coupledwith a grinding action on the solid material.

A conduit 30 is connected to the upper end of the vessel l0 and leads toa pump 3| which may be a rotary sliding vane pump, as shown. The pump 3|discharges through a conduit 35 to a condenser 32 into which a coolingsolution is introduced at 33 and passes out at 34. A by-pass 36 having avalve 31 therein connects the conduits 30 and 35. Thisvalve controls theflow of vapor from the vessel ID to the condenser 32 when the pump 3|vis not in operation. Condensate is collected in a vessel 38.

Assuming that the plastic employed is cellulose acetate and it isdesired to incorporate therein a filler, such as lead carbonate or ironoxide, I Proceed as follows: I first run into the vessel III a solvent,such as acetone, alcohol, or a mixture of ether and alcohol, in anamount about twice that required in the finished product before drying.The pump 22 is then started to bring about a circulation of the solventthrough the pump and the piping system back into the vessel Ill. Thevalve 31 is then opened and the required plasticizers are added throughthe fun-- nel 2| and branch pipe |8 and are circulated through the pump22 until thoroughly dissolved in the solvent. Next, the celluloseacetate is introduced into the confined stream of the solvent in thepipe H by feeding it slowly through cordance with my invention.

the branch conduit II. In passing into the stream and through the pump22, the minute particles of cellulose acetate are each exposed to themaximum quantity of solvent before they have an opportunity toagglomeraie. Thus the cellulose acetate is thoroughly incorporated intothe solent and a smooth, uniform dispersion is made. I have found thatthe required amount of cellulose acetate may thus be thoroughlydissolved in the solvent in around 30 minutes. This time, of course, mayvary with the size of the batch and the size and speed of the pump.

As soon as the cellulose acetate has been thoroughly dissolved, thefilling material is introduced.

through the branch conduit It, being added slowly, the rate of feedbeing controlled by the valve l9, This method of feeding the materialinto a confined stream of solution prevents agglomeration of masses ofmaterial which would otherwise have to be separated by heating. With auniform feed of filling material introduced thus into the plasticsolution, and with the pump 22 running, it will be seen that there mustresult a uniform dispersion of the solid material in the liquid. Inaddition, the action of the gears 23 and 2 grinds the solid materialinto the solution, prevents its lumping, and insures a thorough wettingof every particle of the solid material.

The action of the pump 22 creates a partial vacuum in the intake conduitI, so that a considerable amount of air is drawn into the mixture withthe materials added through the funnel 2|. I have found that the airaids in the rapid mixing which I obtain, and also acts as a carrier forthe solvent which is volatilized in the operation. It also increases thegaseous volume in the vessel i0. Accordingly, while-the mixing isproceeding, the valve 81 is left open to permit the excess mixture ofair and volatilized solvent to pass out of the vessel Hi to thecondenser 32 where a cooling solution chills the solvent and condensesit for recovery in thevessel 38. When the mixing is completed, and withthe circulating pump 22 still in operation, the valve 31 is closed andthe pump II is started, creating a partial vacuum in the vessel Ill anddrawing the solvent out of the mixture to be condensed in the condenser32. By this procedure, I find that I recover about one-half of theoriginal solvent employed, leaving the mixture of a consistency suchthat it may be spread upon a smooth plate to form a sheet, extruded, orotherwis treated, and dried to evaporate the remaining solvent andproduce plates, sheets, rods, or whatever form the final product maytake. It is understood, 0'! course, that the solvent thus evaporated maybe recovered, if desired, by well known means;

When the mixing is completed, the contents of the vessel Ill may bedischarged by means of a valve 40 connected to the conduit l4 directlybeneath the vessel HI.

While the specific example given is a mixture of a cellulosic plastic,one or more solvents, plasticizers and solid filler material, other usesof my invention and other solid-liquid mixtures will at once suggestthemselves to those skilled in the art that may advantageously b mixedin ac- It is well known that the production of a uniform dispersion of arelatively high percentage of filling material in cellulose acetate, orother cellulosic plastics, with thereupon as are specifically set forthin the appended claims.

What I claim is:

1. A process of incorporating solid filler material in plastics whichcomprises forming a solution of the plastic in a volatile solvent,forcibly circulating the solution in a confined restricted path,introducing solid filler material and grinding it into the solutionwhile circulating in said path, maintaining a sub-atmospheric pressurein the path at the point of introduction of the solid material, andevaporating the solvent.

2. In a process of incorporating solid filler material in plastics, thesteps which comprise forming a solution of the plastic, forciblycirculating the solution in a confined path, introducing solid fillermaterial into the solution while circulating in said path, admitting'air to the solution along with the solid material, separating air andvolatilized solvent from the mixture, and condensinl the solvent.

3. A process of incorporating solid filler material in plastics whichcomprises forming a solution of the plastic, forcibly circulating thesolution in a confined path, introducing solid filler material into thesolution while circulating in said path, admitting air to the solutionalong with the solid material, separating air and volatilized solventfrom the mixture, condensing the solvent, and grinding the solidmaterial into the solution as it is introduced thereinto.

4. The method of forming a cellulosic plastic mixture containing up to30% of solid mineral filler by volume, which comprises forciblycirculating a volatile solvent in a confined restricted path, addingcellulosic plastic to the solvent in said path and continuing thecirculation until the plastic is thoroughly dissolved, slowly adding thesolid material to the solution while circulating in said path,submitting the solid material to a grinding action while introducing it,continuing th circulation until the solid material is thoroughlydispersed and maintaining a partial vacuum in the restricted path at thepoint of introduction of the plastic and the solid material to induce aflow of air into the path at said point.

5. The method of forming a cellulosic plastic mixture containing up to30% of solid mineral filler by volume, which comprises forciblycirculating a volatile solvent in a confined path, adding the cellulosicplastic to the solvent in said path and continuing the circulation untilthe plastic is thoroughly dissolved, slowly adding solid filler materialto the solution while circulating in said path, admitting air into thesolution along with the solid material, separating the air andvolatilized solvent from th mixture, and condensing the solvent.

CLARENCE E. BOUTWELL.

